Heat shrink tubing generally comprises a plastic material that is extruded into a tubular form and expanded. The extruded and expanded tube is designed to shrink (i.e., decrease in diameter) when heated to a given temperature. As such, heat shrink tubing can serve various functions. It can provide a tight, protective jacketing to closely cover and insulate various elements (e.g., to protect them from abrasion and to provide thermal, chemical, moisture, and/or electrical insulation); it can serve to bundle certain elements together (i.e., within the same heat shrink tube); it can serve to seal/isolate certain elements from others; it can be used to join/fuse two elements, e.g., two tubes together; and it can serve to modify the properties of an underlying material (e.g., by closing around another material and shrinking that material as well). These capabilities render the tubing useful for various purposes and heat shrink tubing finds use across various fields, e.g., medical, chemical, electrical, optical, electronic, aerospace, automotive, and telecommunications fields.
In the medical context, heat shrink tubing is particularly beneficial in designing increasingly small and more complex devices to be inserted into the body (e.g., catheters, endoscopes, etc.). One representative medical use of heat shrink tubing is in the context of manufacturing a guide catheter, comprising a tubular structure having an inner layer of a polymer, a middle layer of a wire braid and an outer layer of another polymer. To assemble such catheters, an expanded heat shrink tube is typically applied to an assembled shaft around a mandrel and the assembly is exposed to high temperature sufficient to shrink the heat shrink tube. Under these conditions, the outer polymeric layers within the catheter shaft melt and flow, and the heat shrink tube contracts, providing compressive forces such that the inner and outer polymeric layers of the catheter shaft can bond together, encapsulating the wire braid within. The heat shrink tubing is then removed and discarded and the catheter assembly is removed from the mandrel. See, e.g., the disclosures of U.S. Pat. No. 7,306,585 to Ross and U.S. Pat. No. 5,755,704 to Lunn, which are incorporated herein by reference.
Thus, although heat shrink tubing is an essential feature of some final products, in many applications (particularly in medical applications), the heat shrink tubing is involved only in the manufacturing of the final product and is removed from the final product prior to use. Therefore, an additional step involved in the use of heat shrink tubing in certain applications, is removal of the heat shrink tubing from the underlying material. Removability of heat shrunk tubing following use thereof can be facilitated by a score line or indentations/perforations added prior or subsequent to use (i.e., heating) of the heat shrink tubing. After use, the heat shrink tubing can be torn along the scored line or indentations/perforations and discarded. Alternatively, a non-pre-scored heat shrink tube is scored down the length of the tubing following use (i.e., after being shrunk), and the tubing is then torn along the line and discarded.
The nick or score line to facilitate tearing must be at the proper depth to facilitate tearing without damaging the underlying material. If the nick or score line is too deep or if the tubing does not tear perfectly along the score line or indentations/perforations, the medical device can be rendered useless. Accordingly, there is a need for a tubing that can be applied to device components to encapsulate and compress them as needed, wherein the tubing can be readily and reliably removed (even with a non-uniform geometry, which may be difficult to score to a precise depth) with minimal potential to damage the underlying device components.